Recent Advances of Mechanical Science. 145 



two sides, and then a big piece to fill up the gap has to be 

 dropped in between the supporting arms, and the whole struc- 

 ture made equal to carrying its own weight as well as that of 

 passing trains, and bearing the force of the winds, changes of 

 temperature, &c. 



The possibility of making such structures is, I may say, an 

 immediate result of thenew modes of manufacture lately invented 

 for producing the material called " mild steel." The possession 

 of this material has enabled the engineer to achieve results 

 otherwise impossible. It would almost seem as if there was no 

 limit to the size, thickness, and weight of plates which can now 

 be produced by the steel makers. I well remember the time 

 when the size of plate available from iron manufacturers without 

 paying extra was 6 feet long and 2\ feet broad. Any plate over 

 4 cwt. was charged for at a higher rate. It was thought to have 

 been a great step in advance when it was possible to obtain 

 plates 9 feet by 3. At the present time plates up to 30 feet 

 long and 5 feet wide are constantly used in the construction of 

 ships. I may mention that we have had plates delivered nearly 

 4 tons weight and 7 feet broad, and we have also had plates no 

 less than 38 feet long and 3 feet wide for ship work ; and in the 

 manufacture of boilers it is a common thing to find plates dealt 

 with of over 4 tons weight. We have had many delivered 4^ 

 without extra since having to be paid. Rolls for making such 

 plates have now been fitted by Messrs. Spencer, of Newcastle, 

 which are 1 1 feet wide ; in other words, they will be able to 

 produce and finish a plate about 10 feet wide and probably 

 between 30 and 40 feet long, so that we can now obtain plates 

 whose area is twenty times what, within my recollection, it 

 used to be possible to produce. 



What a change has come over the rolling stock, as it is called, 

 during these comparatively few years, from the " Rocket " and 

 " PuflUng Billy " type to such a locomotive as has just been 

 completed and put to work by my friend Mr. Webb, of Crewe, 

 called the " Greater Britain." The average speed at which this 

 locomotive drew a train, the gross weight of which was 382 



